Latexes have been developed for use in printing inks and coatings for applications on a variety of substrates. These latexes are especially suitable as vehicles for coating onto polyolefin surfaces. These materials, designated as "fortified" latexes, provide a number of desirable properties, including mechanical and thermal stability, good processibility and maintenance of viscosity in formulations under high shear conditions. An especially useful latex is the "fortified latex" disclosed and claimed in copending application CIP of Ser. No. 667,662 filed Oct. 9, 1986 and entitled, "Latex Vehicles for Printing Inks and Coatings". Although these latex formulations have proved useful, the occurrence of foaming in ink and coating formulations made with these latexes has been a problem which limits their usefulness.
U.S. Pat. No. 4,820,762 issued to Sheng-Liang Tsaur, discloses a resin-fortified latex polymer prepared by the addition of the resin ". . . to the reaction mixture during the emulsion polymerization i.e., after the initiation of the emulsion polymerization reaction is substantially completed . . . ". This method employs conventional surfactants (anionic or nonionic or combinations of these) which are recommended for emulsion (oil-in-water) polymerizations and known to the art.
The major problem confronting the widespread use of resin fortified latexes in inks and coatings is the occurrence of foaming and insufficient wetting of substrates. Foaming is especially prevalent in inks and coatings applied on a printing press. To overcome these problems, formulators generally add defoamers and wetting agents.
The present invention overcomes these difficulties by using an ammonia salt of a polyelectrolyte resin as the anionic surfactant in combination with a water-in-oil nonionic surfactant as the emulsifier system in an otherwise conventional emulsion polymerization recipe. The polyelectrolyte eliminates the need for anionic surfactants thus simplifying the process. It also imparts exceptional mechanical stability to the latex and ensures the formation of very small particle size. In fact, the products of this invention may be characterized as microemulsions (particle size less than 120 nanometers). The water-in-oil nonionic surfactant reduces the tendency to foam significantly and improves the wetting of substrates.